2,5 Dimethyl-1,4:3,6-dianhydrosorbitol (also known as dimethylisosorbide) exhibits excellent organic solvent characteristics in both water and in other organic solvents, and has many potential uses in pharmaceutical and cosmetic formulations.
In view of important potential pharmaceutical uses for dimethylisosorbide, there is a need for a simple, productive and inexpensive process for its preparation.
Montgomery and Wiggens, J. Chem. Soc. 1946, p. 390-393, reported the methylation of isosorbide with dimethyl sulfate and 30% aqueous sodium hydroxide using water as the solvent. The yield of dimethylisosorbide was reported to be 77%.
Water is not a suitable solvent for the commercial methylation of isosorbide with dimethyl sulfate since this reagent is readily hydrolyzed in the presence of base, resulting in significant yield loss and resultant higher economic outlays. Hydroxylic solvents, such as ethanol, are competitive with the isosorbide in the methylation reaction and provide low or no yields of product while organic solvents such as toluene or methylene chloride are not suitable solvents because the alkali metal salts of isosorbide are not soluble therein.
Therefore, the need exists to uncover a useful process for the preparation of dimethylisosorbide in high yields and at the lowest possible cost.